With the help of the Frame we access the page's BackstackEntry by providing the the sequence number - backStack[<page number>]. In the example above we will navigate back to the initial page and to do that we need to take the first BackstackEntry as follow: topmost().backStack[0]

NB: We start counting the pages from 0. If we need to take the entry for the first page we need to take the it while using the 0 index, for the second 1 index, etc.